1. Field of the Invention
The present invention relates to the field of thermal/wet abatement of gaseous waste streams, and more particularly to a method and system for retrofitting integrated scrubbers to provide maximum oxygen content in a controlled decomposition oxidation abatement process.
2. Description of the Related Art
Semiconductor manufacturing processes utilize a variety of chemicals, many of which have extremely low human tolerance levels. Such materials include gaseous hydrides of antimony, arsenic, boron, germanium, nitrogen, phosphorous, silicon, selenium; silane; silane mixtures with phosphine, argon, hydrogen; organosilanes, halosilanes and other organic compounds. A significant problem has been the removal of these materials from effluent gas streams of semiconductor manufacturing processes. While virtually all U.S. semiconductor manufacturing facilities utilize scrubbers or similar means for treatment of their effluent gases, the technology employed in these facilities is not capable of removing all toxic or otherwise unacceptable impurities.
One solution to this problem is to incinerate the process gas to oxidize the toxic materials, converting them to less toxic forms. Conventional incinerators, however, typically achieve less than complete combustion thereby allowing the release of pollutants to the atmosphere including carbon monoxide (CO) and hydrocarbons (HC). The problem is compounded when the process stream to be treated is composed primarily of a nonflammable gas bearing the undesirable impurities.
A further limitation of conventional incinerators is their inability to mix sufficient combustible fuel with a nonflammable process stream in order to render the resultant mixture flammable and completely combustible. The choice of fuel gas for mixing with a nonflammable process gas is also important from the perspective of maintaining low operating costs, and the incinerator design must reflect this choice of fuel if proper burning characteristics are to be achieved.
However, many incinerators or combustion chambers currently used in existing facilities, depending on their age and construction, are not equipped with adequate piping systems for providing an additional source of flammable fuel gas, such as oxygen or oxygen enriched air. In such situations, several options are available. Retrofitting the existing combustion chamber with additional piping to provide a controlled incineration is one such option, but the cost of this retrofitting may be prohibitive. As another option, a combustible gas may be premixed with the gaseous effluent from the semiconductor process. However, certain exhaust gases from semiconductor processes, such as a silane containing gases tend to ignite spontaneously upon contact with air and this premixing can introduce a hazard potential.
Oxygen or oxygen enriched air may be added directly into the combustion chamber for mixing with the gaseous waste streams containing silane products, however, oxides, particularly silicon oxides are formed and deposited within the combustion chamber and these oxides tend to clog internal nozzles and deposit on the walls. The mass of silicon oxides formed can be relatively large and the gradual deposition with the combustion chamber can necessitate increase maintenance of the equipment.
Accordingly, it would be advantageous to provide an improved method and system to retrofit an existing thermal reactor unit for introduction of a low cost flammable gas, which retrofit is not cost-prohibitive to install on an existing unit, which reduces the release of pollutants to the atmosphere including carbon monoxide (CO), and which deals with the problems of increased deposition of silicon oxides, if formed.
The present invention relates to a method and system for providing controlled combustion of gaseous semiconductor wastes, whereby oxygen and/or an enriched oxygen air stream is introduced into a thermal/wet integrated abatement system to facilitate the conversion of nonflammable mixtures to flammable mixtures and decrease CO emissions without a cost-prohibitive retrofit of the thermal/wet integrated abatement system.
In one aspect, the invention relates to a combustion chamber having increased ability to oxidize virtually all oxidizable components in a gaseous waste stream while effectively and efficiently removing combustion product deposits from the inner wall of the combustion chamber.
Another aspect relates to improved abatement capabilities of a combustion chamber by utilizing existing ducting and adapting same to introduce oxygen or oxygen enriched air for controlled decomposition oxidation of a gaseous waste stream.
Yet another aspect relates to a system and method for incinerating a waste stream of gaseous organic compounds wherein the exhaust gas has reduced amounts of carbon monoxide, and hydrocarbons therein.
Still another aspects relates to a method of reducing carbon monoxide and hydrocarbon emissions from a combustion chamber during the abatement of waste gaseous products which is relatively inexpensive and simple to install and operate.
Thus, in accordance with one aspect of the present invention, there is provided a system for abating gaseous waste material, comprising:
a combustion chamber comprising a chamber cleaning means and at least one gas inlet communicatively connected to a source of compressed air; and
an oxygen separation unit positioned between the gas inlet and source of compressed air.
Another embodiment of the present invention is directed to a thermal reactor for oxidative treatment of gaseous pollutants in a gas stream, the thermal reactor comprising:
a combustion chamber having an entry end comprising at least one inlet for introducing combustible gaseous products and an exit end for removal of combustion products from the combustion chamber;
a hot zone within the combustion chamber located adjacent to said entry end wherein gases entering the combustion chamber react and mix;
an orifice in the combustion chamber communicatively connected to a source of compressed dry air to introduce air into the combustion chamber, the orifice located downstream of the hot zone; and
an oxygen separation unit positioned between the orifice and the source of compressed dry air to provide oxygen and/or oxygen enriched air to the combustion chamber.
The thermal reactor further comprises heating elements that are preferably located annularly about the inner wall of the combustion chamber. The gases exiting the combustion chamber are passed through a liquid vortex that cools the exiting gases, which then are passed through a packed bed for trapping and condensing particles. A liquid scrubber also is provided for removing chemical pollutants. The scrubber may, for example, comprise at least two vertically separated beds containing coated packing.
Preferably, a mechanical scraping means is disposed within the combustion chamber positioned to clean interior surfaces of the combustion chamber to remove buildup of combustion products formed in the combustion chamber. The scraping means comprises a blade apparatus comprising (i) at least one annular mounting member and (ii) at least three scraping blades attached peripherally about the annular mounting member and arranged in a parallel relationship to a longitudinal axis of the chamber; and a reciprocal movement unit for rotating the scraping blade(s) circumferentially back and forth along the interior surface of the chamber to clean the interior surface of the chamber, wherein such reciprocable movement unit comprises a reciprocable member pivotally connected to an extension member, and the extension member is pivotally connected at a peripheral position to the blade apparatus.
The mechanical scraping means and the liquid vortex unit are suitably combined into a unitary assembly.
In one aspect, the liquid vortex comprises a baffle that may be arranged to provide a flow restriction so that during some operations of cleaning the interior of the combustion chamber may be filled with liquid, preferably water, to enhance removal of scraped products from the chamber.
A compressor is communicatively connected to the orifice which is centrally positioned within the combustion chamber of the thermal reactor to supply a source of compressed air to the oxygen separation device positioned downstream of the compressor and upstream of the thermal reactor. The compressor is used to assist in pressurizing the air flow being delivered to the oxygen separation unit, or in a subatmospheric oxygen enrichment system, utilized to increase the pressure of the oxygen-enriched stream at a location downstream of the oxygen separation unit.
The oxygen separation unit of the present invention may comprise any device with selectivity for separating one major gaseous component from the other major components in the feed gas mixture. For example, a single membrane device or alternatively a several membrane device may be provided and operated to achieve a separation of the gaseous components in air. Typically, the membrane devices are manufactured in modules, each having certain semi-permeable membrane areas for permeation. Semi-permeable membrane materials currently available which can be employed in this process include: polysulfone, cellulose acetate, polyimide, polyamide, silicone rubber, polyphenylene oxide, ceramic materials, etc.
Preferably, a ceramic material having a high selectivity for oxygen is utilized in the oxygen separation device to efficiently sorptively remove oxygen from an oxygen-containing feed gas mixture, to produce extremely high product gas purity. The ceramic material may be used as a filler material in a separation module or as a coated substrate, e.g., at least a portion of a membrane or fiber surface is coated with the oxygen-adsorbent ceramic material.
The ceramic material may comprise at least one material such as:
oxide fluorite oxygen ion conductors of the formula A4O8;
pyrochlore material of the formula A2B2O7;
material of the formula Bi2O3(A2O6);
stabilized forms of d-Bi2O3;
Bi24Pb5Ca3O44;
Bi14V2O11;
perovskite materials of the formula ABO3;
oxide Brown Millerite electrolytes of the formula A2B2O5;
mixed Brown Millerite electrolytes of the formula ABO3ABO2.5;
A4O6ABO2.5 compositions;
mixed superconducting (ABO3AO) electrolytes;
cryolite (A3BO3) electrolytes;
columbite (AB2O6) electrolytes;
and corresponding doped materials,
wherein A and B are metals independently selected from the group consisting of lanthanum, aluminum, strontium, titanium, calcium, zirconium, iron, barium, indium, gadolinium, yttrium, copper, cerium, thorium, bismuth, cobalt, nickel, magnesium, manganese, vanadium, chromium, niobium, tantalum, boron, haffiium, neodymium, terbium, ytterbium, erbium, thullium, lutetium, samarium, lead, tin, lawrencium, and praseodymium.
A further aspect of the invention relates to a method of forming ceramic-coated fiber, wherein the ceramic is a metal oxide ceramic including at least one metal having a xe2x80x9chigh adsorptive capacityxe2x80x9d at elevated temperatures, in which the method comprises the steps of:
(a) reacting nitric acid and ethylene glycol to yield glycolic acid;
(b) heating the glycolic acid to form oxalate ion;
(c) reacting the oxalate ion with the at least one metal to form a sol gel comprising corresponding metal oxalate(s);
(d) depositing the sol gel on a fiber substrate; and
(e) calcining the sol gel on the fiber substrate to form a corresponding ceramic coating and yield the ceramic-coated fiber.
As used herein, the term xe2x80x9chigh adsorptive capacityxe2x80x9d means an oxygen storage capacity of at least 40 millimoles of oxygen per mole of the ceramic material when the ceramic material is contacted with oxygen gas at a temperature of 800xc2x0 C.
As used herein, the term xe2x80x9celevated temperaturexe2x80x9d means a temperature in the range of from 500xc2x0 C. to 1000xc2x0C.
When metal oxide ceramics are referred to herein in symbolic notational form without stoichiometric subscripts (e.g., in the term LaCaCoMO), it is to be understood that the respective elemental constituents are present in such material in stoichiometrically appropriate proportions relative to one another.
In another aspect, the invention relates to a method for generating oxygen-enriched air for subsequent introduction into an integrated scrubber system that comprises a combustion chamber for abatement of gaseous waste products from a semiconductor process. The method includes the steps of:
providing an oxygen and nitrogen separation system to effect separation of air into at least a nitrogen gas component and an oxygen gas component;
introducing compressed air into an inlet of the oxygen and nitrogen separation system;
withdrawing the nitrogen component from the oxygen and nitrogen separation system;
withdrawing the oxygen component from the oxygen and nitrogen separation system; and
introducing the oxygen component into the combustion chamber for mixing with the gaseous waste products for abatement therein.
Yet another aspect of the present invention relates to a method for retrofitting an abatement system for processing a gaseous waste stream to introduce an oxygen or nitrogen enriched source therein, the method comprising:
providing an oxygen and/or nitrogen enriching device communicatively connected to an abatement chamber;
introducing compressed dry air to the oxygen and/or nitrogen enriching device wherein the compressed dry air is separated into an oxygen rich gaseous component and a nitrogen rich gaseous component; and
directing and introducing the oxygen or nitrogen enriched gaseous component to the abatement chamber.
The method of retrofitting may further comprise:
providing a mechanical scraping device to remove combustion products deposited during the processing of the gaseous waste stream wherein the mechanical scraping device comprises:
(i) at least one annular mounting member;
(ii) at least three scraping blades attached peripherally about the annular mounting member and arranged in a parallel relationship to a longitudinal axis of the chamber; and
(iii) a reciprocal movement unit for rotating the scraping blade(s) circumferentially back and forth along the interior surface of the chamber to clean the interior surface of the chamber, wherein such reciprocable movement unit comprises a reciprocable member pivotally connected to an extension member, and the extension member is pivotally connected at a peripheral position to the blade apparatus.
Other aspects, features and embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.